ELECTRIC TRACTION

INTRODUCTION: The locomotion in which the driving force is obtained from electric motor is called the electric traction system. There are various system of electric traction existing such as electric train, trolley buses, diesel-electric vehicles and gas turbine electric vehicles

Electric traction system

MAJOR CLASSIFICATIONs OF traction Non-electric traction: examples steam engine drive ic engine drive Electric traction: diesel electric drive gas turbine electric drive

Requirements of an ideal traction system The starting tractive effort should be high so as to have rapid acceleration. The wear on the track should be minimum. The equipments should be capable of withstanding large temporary loads. Speed control should be easy. Pollution free. Low initial and maintenance cost. The locomotive should be self contain and able to run on any route.

Merits of electric traction High starting torque. Less maintenance cost Cheapest method of traction Rapid acceleration and braking Less vibration Free from smoke and flue gases hence used for underground and tubular railway.

Demerits of electric traction High capital cost. Problem of supply failure. The electrically operated vehicles have to move on guided track only. Additional equipment is required for achieving electric braking and control.

Different systems of traction: Direct steam engine drive Direct IC engine drive Steam electric drive IC engine electric drive Petrol electric traction Battery electric drive Electric drive

IC ENGINE ELECTRIC DRIVES

Supply Systems for Electric traction: D.C system A.C system Single phase Three phase Composite system Single phase AC to DC Single phase to three phase

Speed time curve for train movement Acceleration Constant acceleration Speed curve running Free run or constant speed period Coasting period Retardation or braking period

Typical speed time curves for different services Urban or city services Sub urban services Main line services TYPES OF SPEED IN TRACTION crest speed Average speed Schedule speed

Factors affecting energy consumption Distance between the stops. Train resistance Acceleration and retardation. Gradient train equipment.

Traction motors DC series motor Ac series motor Three phase induction motor

Traction motor electrical features High starting torque Simple speed control Regenerative braking Better commutation Capability of withstanding voltage fluctuations. MECHANICAL FEATURES Light in weight. Small space requirement. Robust and should be able to withstand vibration.

Traction motor control Rheostat control Series parallel control Field control Buck and boost method Metadyne control Thyristor control Phase control Chopper control

Braking ELECTRIC BRAKING Plugging or reverse current braking Rheostatic braking Regenerative braking DC shunt motor DC series motor Induction motor MECHANICAL BRAKING Compressed air brakes Vacuum brakes MAGNETIC TRACK BRAKES

Recent trends in electric traction Tap changer control Thyristor control Chopper control Micro processor control

Micro processor control

Questions ?

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